1. Field of the Invention
The present invention generally relates to an optical disk device. More specifically, the present invention relates to an optical disk device that reproduces various types of optical disks.
2. Background Information
Optical disks are widely used as data recording media with which a large volume of data can be accessed at high speed and low cost and without contact. Specifically, the optical disks are widely used as data recording media for personal computers and for recording and reproduction of digital audio data and digital video data. In particular, next-generation optical disks (Blu-ray Disc (BD®), HD-DVD®, etc.) have been proposed in recent years as rewritable optical disks with high-volume. Along with this, there has been a desire for an optical disk device that records and reproduces information to and from various types of optical disks, such as a CD, a DVD®, and the next-generation optical disks. Thus, with the optical disk device, it is necessary to reliably identify the type of the optical disk mounted in the optical disk device.
A conventional optical disk device includes a three-wavelength compatible objective lens to handle three wavelengths corresponding to the types of the optical disks. Specifically, the conventional optical disk device handles three kinds of laser beams having different wavelengths to record and reproduce information. With the three-wavelength compatible objective lens, an optical head installed in the optical disk device can be made compact.
The three-wavelength compatible objective lens handles three kinds of laser beams having different wavelengths, namely, 780 nm for the CD, 650 for the DVD, and 405 nm for the next-generation optical disk. In the physical structure of the optical disks, the distance from a disk surface to an information recording face is 1.2 mm for the CD, 0.6 mm for the DVD, and 0.1 mm for the next-generation optical disk. However, the three-wavelength compatible objective lens makes it possible to control focus for all of the optical disks.
With the three-wavelength compatible objective lens, the optical head can be made smaller. Each of focus distances is different for each of the wavelengths. Thus, when the three-wavelength compatible objective lens is employed in the optical disk device, the type of the optical disk mounted in the optical disk device can be misidentified, particularly because of variance in the sensitivity characteristics of optical elements of the optical pickup.
Japanese Laid-Open Patent Application Publication No. 2005-25952 discloses a method for identifying an optical disk mounted in an optical disk device having a three-wavelength compatible objective lens. With the optical disk device, information is recorded or reproduced by selectively irradiating an information recording face of the optical disk via the three-wavelength compatible objective lens with laser beams of three different wavelengths for the CD, the DVD and the BD. When a disk identification processing is commenced, first, the BD laser is flashed (Step S1). A position of a beam expander for correcting spherical aberration is set to a position for the BD (Step S2). Then, a focus search processing is performed (Step S3). During the focus search processing, a focus search time from when the reflected light from the disk surface of the optical disk is detected to when the reflected light from the information recording face is detected is measured. Then, it is determined whether or not the focus search time is less than a predetermined value (Step S4). If the focus search time is less than the predetermined value, then the optical disk is determined to be the BD. If the focus search time is greater than the predetermined value, then the DVD laser is flashed (Step S5). Then, it is determined whether or not the mounted optical disk is the DVD in the same manner as in the processing of steps S1 to S4. If it is determined that the mounted optical disk is not the DVD, then the CD laser is flashed. The position of the beam expander is set to a position for the CD. Then, the focus search processing is performed. It is determined whether or not the mounted optical disk is the CD. If it is determined not to be the CD, then it is determined that there is no disk.
As discussed above, the technology discussed in Japanese Laid-Open Patent Application Publication No. 2005-25952 involves detecting the difference in distances from the disk surface to the information recording face, which is a difference in the physical structures of the optical disks, based on the focus search time. Specifically, the focus search time is compared with the predetermined value. As a result, the type of optical disk mounted in the optical disk device is identified. As mentioned above, the distance from the disk surface to the information recording face decreases in the order of CD>DVD>BD, so the focus search time from the disk surface to the information recording face as measured by the focus search processing similarly decreases in the order of CD>DVD>BD. This relationship is used to set the predetermined values for identifying three types of the optical disks by comparing the predetermined values with the focus search time.
With the conventional optical disk device discussed in Japanese Laid-Open Patent Application Publication No. 2005-25952, the predetermined values for performing the disk identification processing are set as values of time. Specifically, the focus search time is measured. Then, the predetermined values, that are values of time, are used as thresholds for comparing with the focus search time. As a result, the type of the optical disk is identified. In this case, the focus search time becomes shorter or longer depending on variance in motor torque at which the focus search processing is driven, or in the light receiving sensitivity of a light receiving element of the optical disk device. Therefore, the predetermined values used for the disk identification processing are set by taking into account the variance between individual optical disk devices. However, it is difficult to keep up with the variance among mass-produced optical disk devices. Thus, it is difficult to correctly identify the type of the optical disk mounted in the optical disk device. With another method, the sensitivity of a focus actuator can be adjusted to maintain constant focus search speed and account for the above-mentioned variance during producing the optical disk device. However, additional step to adjust the sensitivity of the focus actuator is needed.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved optical disk device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.